标签：定义 display 允许 const cti park code 抽象 .com
1.定义
允许一个对象在其内部状态改变时改变它的行为，对象看起来似乎修改了它的类。例如：在一个停车场
有很多的停车位，停车位有三种状态，分别是忙碌，空闲，维护。如果不使用状态模式的话，那么状态的改
是停车位去维护，这样的话不符合单一自责原则，停车位的职责过重，而且如果新增状态要修改停车位的代
码，也违背了开闭原则。正确的做法是将状态抽象出来，停车位的状态改变让具体的状态类去维护，这样的
话就更加具有灵活性。
2.模式结构
（1）多状态类：ParkingSeat
（2）抽象状态：ParkingSeatState
（3）具体状态类：BusyParkingSeatState（忙碌）FreeParkingSeatState（空闲）MaintainParkingSeatState（维护）
3.代码
（1）ParkingSeat.java
package com.uptowncat.state; /** * 停车位 * * @author Administrator * */ public class ParkingSeat { private int id; private String sequenceNum; private ParkingSeatState state; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getSequenceNum() { return sequenceNum; } public void setSequenceNum(String sequenceNum) { this.sequenceNum = sequenceNum; } public ParkingSeatState getState() { return state; } public void setState(ParkingSeatState state) { this.state = state; } public ParkingSeat(int id, String sequenceNum, ParkingSeatState state) { super(); this.id = id; this.sequenceNum = sequenceNum; this.state = state; } /** * 状态转换：0 busy, 1 free, 2 maintain * @param stateNum */ public void change(int stateNum) { state.change(stateNum); } }
（2）ParkingSeatState.java
package com.uptowncat.state; /** * 抽象的停车位状态 * @author Administrator * */ public abstract class ParkingSeatState { protected String name; protected ParkingSeat seat; public void change(int stateNum) { // TODO Auto-generated method stub check(stateNum); } public abstract void check(int stateNum); public ParkingSeatState(String name, ParkingSeat seat) { super(); this.name = name; this.seat = seat; } public String getName() { return name; } public void setName(String name) { this.name = name; } public ParkingSeat getSeat() { return seat; } public void setSeat(ParkingSeat seat) { this.seat = seat; } }
（3）FreeParkingSeatState.java
package com.uptowncat.state; /** * 空闲状态 * @author Administrator * */ public class FreeParkingSeatState extends ParkingSeatState { public FreeParkingSeatState(String name, ParkingSeat seat) { super(name, seat); // TODO Auto-generated constructor stub } @Override public void check(int stateNum) { // TODO Auto-generated method stub if(stateNum == 0) { ParkingSeatState busyState = new BusyParkingSeatState("busy", seat); seat.setState(busyState); }else { if(stateNum == 2) { ParkingSeatState maintainState = new MaintainParkingSeatState("maintain", seat); seat.setState(maintainState); } } } }
（4）BusyParkingSeatState.java
package com.uptowncat.state; /** * 忙碌状态 * @author Administrator * */ public class BusyParkingSeatState extends ParkingSeatState { public BusyParkingSeatState(String name, ParkingSeat seat) { super(name, seat); // TODO Auto-generated constructor stub } @Override public void check(int stateNum) { // TODO Auto-generated method stub if(stateNum == 1) { ParkingSeatState freeState = new FreeParkingSeatState("free", seat); seat.setState(freeState); }else { if(stateNum == 2) { ParkingSeatState maintainState = new MaintainParkingSeatState("maintain", seat); seat.setState(maintainState); } } } }
（5）MaintainParkingSeatState.java
package com.uptowncat.state; /** * 维护状态 * @author Administrator * */ public class MaintainParkingSeatState extends ParkingSeatState{ public MaintainParkingSeatState(String name, ParkingSeat seat) { super(name, seat); // TODO Auto-generated constructor stub } @Override public void check(int stateNum) { // TODO Auto-generated method stub if(stateNum == 1){ ParkingSeatState freeState = new FreeParkingSeatState("free", seat); seat.setState(freeState); }else { if(stateNum == 0) { try { throw new Exception("维护状态不能直接变为忙碌状态！"); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } } } }
（6）Client.java
package com.uptowncat.state; import org.junit.Test; /** * 单元测试 * @author Administrator * */ public class Client { @Test public void test() { ParkingSeat parkingSeat = new ParkingSeat(1, "seat A", null); ParkingSeatState freeState = new FreeParkingSeatState("free", parkingSeat); parkingSeat.setState(freeState); System.out.println("初始状态是："); print(parkingSeat); parkingSeat.change(0); print(parkingSeat); parkingSeat.change(2); print(parkingSeat); parkingSeat.change(0); print(parkingSeat); } public void print(ParkingSeat parkingSeat) { System.out.println(parkingSeat.getSequenceNum() + " 的状态是： " + parkingSeat.getState().getName()); System.out.println("--------------------------------------"); } }
4.优缺点
优点：
（1）封装了转换规则，具有多状态的对象当状态发生改变时能够自动切换状态
（2）枚举可能的状态，但要确定状态的种类
（3）能够方便地新增新的状态，只需要改变对象状态就可以改变对象的行为
（4）可以避免使用庞大的if...else语句块去改变状态
（5）可以让多个环境对象共享一个状态对象，从而减少系统中对象的个数
缺点：
（1）状态模式的使用必然会增加系统中类和对象的个数，在一定程度上会增加系统的复杂度
（2）状态模式的实现较为复杂，如果使用不恰当会造成程序结构和代码混乱
（3）状态模式对”开闭原则“支持并不太好，新增状态类时可能要适当地修改原有的状态类的转换逻辑
Practice makes perfect!
标签：定义 display 允许 const cti park code 抽象 .com
原文地址：http://www.cnblogs.com/uptowncat/p/7224257.html
